A fixed magnetic disk drive unit reads and writes signals while its magnetic head floats low (with a gap in the submicron order) over its magnetic disk rotating at a high speed. A conventional magnetic disk used in a fixed magnetic disk drive unit has been manufactured by laminating a magnetic layer and a protective layer on a flat substrate of nonmagnetic material, for example, aluminum or glass. In recent years, some of the fixed magnetic disk drive units have been using a pre-embossed type magnetic disk that records preformatted information, such as servo information in the uneven patterns formed on the substrate. Nikkei Electronics No. 586 (7 Jul. 1993) for example discloses a fixed magnetic disk drive unit using a pre-embossed medium that carries servo patterns and recording tracks formed with uneven patterns on a glass substrate. In the servo pattern of the medium, pits of an uneven or non-uniform pattern are magnetized in the opposite direction along the track line. The magnetic head reads a signal pattern of 1/0 by detecting or sensing leakage magnetic flux at the boundary of the main surface and the pit.
Servo information and recording tracks of the pre-embossed magnetic disk can be formed with high precision because the information and the tracks are manufactured by a method similar to the method in the optical disk production. The pre-embossed systems are expected to be applied to a ROM disk storing programs or data, as well as the application to the servo pattern. Presently, image data, sound data, and various software data (hereinafter, referred to as “contents”) are distributed through networks, such as the internet. Fixed magnetic disk drive units or memory cards are used for temporarily storing the data of these contents that are bought and downloaded.
With increase in the distributing quantity of the digital contents, digital copyright management systems have been introduced for protecting the contents. A digital copyright management system performs a certain operation on the purchased contents to prevent transferring of a copy of the contents to a third party, and uploading and delivering to the internet.
Some digital copyright management systems provide a scheme that generates a key based on hardware information of the client's PC that playbacks the contents, and that does not permit playback without the key. An example of such a system working jointly with a smart card (a memory card capable of intelligent functions) uses hardware ID information that is embedded in the smart card and unique to the card. This ID information is embedded in an unmanipulatable condition, which enhances security.
Present fixed magnetic disk drive units do not use such ID information embedded in the medium. One of the reasons is because the structure of the fixed magnetic disk drive unit is designed to allow rather easy rewriting of data. Embedding ID information using a magnetic head with software can hardly prevent one from manipulating the ID information. One way to solve that problem is by physically embedding ID information like the above-mentioned pre-embossed type magnetic disk. However, the pre-embossed type magnetic disk formed by a stamper has a problem in that the magnetic disks formed by the same stamper have the same ID information. That is, uniqueness of ID information cannot be obtained in a mass production scale. Accordingly, there is a need to provide a magnetic disk medium that can be embedded with unmanipulatable ID information, while also being able to record unique ID information. The present invention addresses this need.